RANEY Ni catalyzed transfer hydrogenation of levulinate esters to γ-valerolactone at room temperature

Article abstract of DOI:10.1039/c3cc40980e

A catalytic transfer hydrogenation process was developed for the production of γ-valerolactone (GVL) from ethyl levulinate (EL) and a H-donor at room temperature. Ethyl levulinate was almost quantitatively converted to γ-valerolactone. Further, a two step process for producing GVL from biomass derived platform molecules was also reported. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3cc40980e

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RANEYs Ni catalyzed transfer hydrogenation of
levulinate esters to c-valerolactone at room
temperature†
Cite this: Chem. Commun., 2013,
49, 5328
Received 5th February 2013,
Accepted 23rd April 2013
Zhen Yang,z Yao-Bing Huang,z Qing-Xiang Guo* and Yao Fu*
DOI: 10.1039/c3cc40980e
www.rsc.org/chemcomm
A catalytic transfer hydrogenation process was developed for the
production of c-valerolactone (GVL) from ethyl levulinate (EL) and a
H-donor at room temperature. Ethyl levulinate was almost quantitatively
converted to c-valerolactone. Further, a two step process for producing
GVL from biomass derived platform molecules was also reported.
The gradual depletion of fossil fuel resources has stimulated the
global efforts to search for alternative sources, for the sustainable
production of fuels and chemicals. Lignocellulosic biomass is an
abundant and renewable source of carbon that allows the produc-
tion of versatile and viable chemicals.1 Various processes including
gasification, fermentation, hydrogenolysis and chemical transforma-
tion have been developed for the conversion of lignocellulosic
Scheme 1 Reduction of LA and its esters to g-valerolactone.
biomass and its derivatives into value-added platform molecules of LA. Thus, it is attractive to establish a new route to produce
and biofuels.2,3 Among these molecules, GVL is considered as one of GVL from levulinate esters.9
the most appealing molecules which could be used as a fuel
additive, solvent, and liquid fuel.4 Furthermore, GVL is an ideal different levulinate esters. Rode and Hengne10 prepared the Cu/ZrO2
precursor for the production of alkanes and valuable chemicals.5
and Cu/Al2O3 catalysts for the conversion of LA to GVL in methanol
Several groups have reported the production of GVL from
Many processes have been reported for the production of GVL solvent. In the reaction, methyl levulinate was firstly formed and
from lignocellulose (Scheme 1). The hydrogenation of levulinic then hydrogenated into GVL at 200 1C and 500 psi H2. In 2011, Cao
acid (LA) to GVL using H2 gas was generally conducted in vapor- et al.11 used butyl levulinate and formate esters, alcoholized from
phase, liquid-phase, super critical CO2 or biphasic systems with cellulose, to produce GVL over the Au/ZrO2 catalyst. The yield of GVL
various metal catalysts such as Ir, Rh, Pd, Ru, Pt, Re, Ni.6 Recently, was up to 95% at 170 1C. In order to avoid the use of precious
formic acid (FA) was used as an in situ hydrogen source for the metals, Dumesic and Chia12 reported a catalytic transfer hydro-
conversion of LA to GVL instead of external H2 gas. The acid genation (CTH) process to convert LA and its esters into GVL with
catalyzed dehydration of carbohydrates gave a mixture of LA and base metal catalysts ZrO2 and the hydrogen donor isopropanol at
FA. The utilization of the mixture to produce GVL was a more 150 1C under inert gas.
economic way which would avoid the costly separation of LA
The catalytic transfer hydrogenation (CTH) method has emerged
and make the process more atom economical.7 Apart from LA, as an efficient and simple tool for the reduction of biomass derived
levulinate esters were considered as alternative substrates for molecules in the presence of hydrogen donors (e.g. isopropanol
producing GVL under reductive conditions.8 Actually, the produc- (2-PrOH)).13 Fukuoka et al.14 reported a CTH process for the
tion of levulinate esters from lignocellulosic biomass gave higher conversion of cellulose to sugar alcohols with Ru/C as the catalyst
product yields and easier product separation than the production and 2-PrOH as the hydrogen donor, the yield of the sugar alcohols
was up to 47%. Rinaldi and Wang15 developed a CTH method
for upgrading aromatic and phenolic feeds with RANEYs Ni
and 2-PrOH. The reaction was operated under relatively mild
Anhui Province Key Laboratory of Biomass Clean Energy, Department of Chemistry,
University of Science and Technology of China, Hefei 230026, PR China.
E-mail: fuyao@ustc.edu.cn, qxguo@ustc.edu.cn
conditions and various hydrogenated products were obtained.
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
Overall, the CTH method provides a new option for the selective
reduction of biomass derived molecules.
c3cc40980e
‡ The authors contributed equally to the work.
c
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Herein, we report a CTH process for the production of GVL catalyst was kept for one week before use, the GVL yield was 95%
from ethyl levulinate and secondary alcohols over RANEYs Ni (Table 1, entry 15). Besides, if the freshly prepared catalyst was kept
catalyst. The reaction could be conducted at room temperature in water, the yield decreased to 87%, showing a negative effect of
with an almost quantitative yield of GVL. To the best of our H2O on the reaction (Table 1, entry 16). The catalysts (stored in
knowledge, this is the mildest condition for the production of water) purchased from the reagent company also gave an unsatisfied
GVL using CTH methods. The catalyst can be reused at least five results (Table 1, entry 17). Other reaction parameters were also
times and can maintain a good catalytic activity. Moreover, a two optimized such as reaction time, solvent and catalyst loading (see
step process was presented for the production of GVL from ESI†). With regard to the stability of RANEYs Ni in the CTH process,
biomass derived platform molecules such as fructose and HMF.
the catalyst was recycled and reused five times without much drop in
In the initial studies, a variety of Ni based catalysts such as the activity (Table S3.3 in ESI†).
Ni/TiO2, Ni/SiO2, Ni/CeO2, Ni/C and RANEYs Ni were prepared
The hydrogen donor plays an important role in the CTH
and tested in the CTH reaction (Table 1, entries 1–5). To process which provides the H-atoms for the reduction. Thus,
our surprise, the reaction with RANEYs Ni catalyst gave an various primary and secondary alcohols were also evaluated as the
almost quantitative yield of GVL at 80 1C for 9 h. In contrast, H-donors (Table 2). The blank experiment without the H-donor
other supported Ni catalysts showed no catalytic activity. For gave a 23% yield of GVL (Table 1, entry 1). It was probably due to
comparison, noble metal based catalysts were also evaluated in the hydrogen adsorbed in the nickel skeleton during the prepara-
the CTH processes and the reaction using the Ru/C catalyst tion process. After the reaction finished, the catalyst was filtered
achieved a better performance than the others which was in and reused in the blank experiment. The yield of GVL was only 1%
accordance with the previous work that Ru/C was an efficient which confirmed the above speculation (Table 2, entry 2). Experi-
catalyst for the CTH process (Table 1, entries 6–9).16 In order to ments with primary alcohols such as methanol, ethanol and
further reduce the energy input for the CTH process, the CTH 1-PrOH showed similar performances to the blank experiments
reactions were carried out at room temperature (B25 1C). (Table 2, entries 3–5). Clearly, the primary alcohols were negative
Among these catalysts, RANEYs Ni catalyst maintained a high hydrogen donors for CTH processes.15 The secondary alcohols
catalytic activity at lower temperature while the Ru/C catalyst exhibited better performances, the CTH reaction with 2-BuOH
only gave a decreased yield of 27% (Table 1, entries 10–12). gave a similar result to that with 2-PrOH (Table 2, entries 6–8).
Further reducing the reaction to 2 h led to a slight decrease in However, the reaction with cyclohexanol gave poor results, which
the GVL yield (87%) (Table 1, entry 13). Besides, when the was probably due to its high viscosity that prevented the full
reaction was conducted in air, only 69% yield of GVL was mixing of the catalyst and the substrates.
obtained which suggested that the RANEYs Ni catalyst was
The different activities of the two kinds of alcohols in the
sensitive to air and quickly lost its catalytic activity during the CTH reactions were probably related to their different reaction
reaction (Table 1, entry 14). During the optimization, freshly pathways. Previous surface studies on the poisoning effect of
prepared RANEYs Ni catalyst showed the highest activity. If the primary alcohols on Ni (111) and Ni (100) surfaces revealed that
the adsorption of MeOH or EtOH involves the cleavage of the
O–H bond and generates a surface alkoxy group which would
block the RANEYs Ni surface.15,17 In contrast, the secondary
alcohols are easily undergoing the b-H elimination step after
the generation of an alkoxy group on the Ni surface. During the
elimination process, a ketone molecule was released and two
H-atoms remained on the Ni surface which were the active
species for transfer hydrogenation.15,18 After hydrogenation,
the RANEYs Ni catalyst regenerated (Scheme 2).
Table 1 Optimization of the CTH reaction conditionsa
Entry
Catalysts
T [1C]
Solvent
Yield (%)
1
2
3
4
5
6
7
8
Ni/TiO2
Ni/SiO2
80
80
80
80
80
80
80
80
80
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
2-PrOH
0
0
0
1
>99
0
Ni/CeO2
Ni/C
Having established the CTH route for the production of GVL from
ethyl levulinate and 2-PrOH, we next turn to the conversion of biomass
RANEYs Ni
Au/C
Pd/C
Pt/C
1
Table 2 Various H-donors for the CTH processesa
32
93
>99
1
27
87
69
95
87
57/68
9
Ru/C
10
11
12
13b
14c
15d
16e
17f
RANEYs Ni
Pt/C
Entry
Solvent
GC yield (%)
Ru/C
1
2b
3
4
5
6
7
8
—
—
18
1
RANEYs Ni
RANEYs Ni
RANEYs Ni
RANEYs Ni
RANEYs Ni
MeOH
EtOH
1-PrOH
2-BuOH
Cyclohexanol
2-PrOH
24
27
28
92
35
99
a
1 mmol EL, catalyst (5 wt%) 30 mg, RANEYs Ni (freshly prepared and
kept in 2-PrOH, wet, 0.1 g), room temperature, Ar. The yield was
determined by GC using diethylene glycol dimethyl ether as the internal
a
Reaction conditions: EL (1 mmol), RANEYs Ni (freshly prepared and
b
c
d
standard. Reaction time 2 h. In air. The catalyst was kept in kept in 2-PrOH, wet, 0.1 g), solvent (2 ml), room temperature, Ar, 9 h. b The
e
2-ProH for 1 week before use. Freshly prepared catalyst and kept in catalyst for the second run from entry 1. The yield was determined by GC
f
water. RANEYs Ni slurry in water, purchased from TCI/Aladdin.
using diethylene glycol dimethyl ether as the internal standard.
c
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temperature but also offers a possibility of applying this method
in the large-scale industrial production of GVL from biomass.
Further effort will be devoted in the exploration of milder
systems for the production of GVL from biomass.
We thank the 973 Program (2012CB215305), NSFC (21172209)
and CAS (KJCX2-EW-J02) for the financial support.
Notes and references
Scheme 2 Production of active species with 11 and 21 alcohols.
Table 3 Various H-donors for the CTH processes
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Substrate
Alcohols
EL yield (%) H-donor
GVL yield (%)
1
2
3
FAL
HMF
Fructose
EtOH
EtOH
EtOH
95
74
55
2-PrOH
2-PrOH
2-PrOH
86
66
50
a
b
Substrate 1 mmol, solvent 2 ml, Amberlyst-15 30 mg, 120 1C, 20 h.
RANEYs Ni (freshly prepared and kept in 2-PrOH, wet, 0.1 g), Ar,
room temperature, 9 h.
derived platform molecules (furfural alcohol (FAL), HMF and fructose)
(Table 3). The process involves two steps: (1) alcoholysis of the
molecules into EL; (2) CTH of EL into GVL. For the alcoholysis
of platform molecules, solid acids were chosen as the catalysts
and ethanol was used as the solvent. Among the acid catalysts,
Amberlyst-15 showed the highest catalytic activity (see ESI†).19
The yields of EL from furfural alcohol, HMF and fructose were
95%, 74% and 55%, respectively. After the alcoholysis reaction,
RANEYs Ni catalyst was directly added to the mixture at room
temperature, however, the results were extremely low. The
catalyst was probably poisoned by the humins formed during
the alcoholysis process. Instead, EL was separated by vacuum
distillation and subsequently subjected to reduction in 2-PrOH.
The overall yields of GVL for the three platform molecules were
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separated by vacuum distillation. Both of the solvents (ethanol
and 2-PrOH) and the catalyst (Amberlyst-15 and RANEYs Ni)
could be recycled after filtration and distillation.
In conclusion, we have reported a mild catalytic transfer
hydrogenation process for the production of GVL from ethyl
13 G. Yi and Y. G. Zhang, ChemSusChem, 2012, 5, 1383.
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at room temperature over a RANEYs Ni catalyst, yielding a >99%
of GVL. The catalyst could be reused five times without much
17 (a) D. Almawlali and J. M. Saleh, J. Chem. Soc., Faraday Trans. 1,
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to GVL by a two step process with moderate yields. The new CTH
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c
5330 Chem. Commun., 2013, 49, 5328--5330
This journal is The Royal Society of Chemistry 2013